Most wheeled motor vehicles include some form of passive suspension system including leaf or coil springs to absorb shocks caused by road irregularities, such as bumps and pot holes, and dampers to attenuate the resultant spring oscillations. Although many modern passive suspension systems can afford an acceptable compromise between comfort and performance, tuning a suspension for comfort typically results in decreased performance and vice versa. Further, passive suspension systems typically are not able to anticipate cornering or braking loads and can only react to such loads after they are imparted to the vehicle.
Semi-active suspensions have been developed which achieve a better compromise of comfort and performance by affording variable damper calibration. Other semi-active or active systems use gas-over-oil hydraulic struts. Such systems typically use conventional hydraulic fluid, which generally is considered to be incompressible, in conjunction with a pressurized gas to effect spring function. In such systems, the pressurized gas, and not the fluid, acts as a spring